MySQL (CentOS 6.7) password not changing (blank)?

Question

MySQL

Hi all!
I tried in every way to change the password from root "and,
When checking
mysql>
-> use * databasname *
-> select Host, User, Password, authentication_string;
everything is fine,
Even when I go to mysql> (mysql -u root -p) requires a password , I enter and go in, everything
is fine. But anyway, in mysql tuner it says that root has an empty password:

spoiler

-------- General Statistics --------------------------------------------------
[--] Skipped version check for MySQLTuner script
[OK] Currently running supported MySQL version 5.5.49-log
[OK] Operating on 64-bit architecture

-------- Storage Engine Statistics -------------------------------------------
[--] Status: -Archive -BDB -Federated +InnoDB -ISAM -NDBCluster
[--] Data in InnoDB tables: 43M (Tables: 615)
[--] Data in PERFORMANCE_SCHEMA tables: 0B (Tables: 17)
[!!] Total fragmented tables: 15

-------- Security Recommendations  -------------------------------------------
[!!] User 'root' has no password set.

-------- Performance Metrics -------------------------------------------------
[--] Up for: 1d 23h 40m 7s (1M q [7.469 qps], 7K conn, TX: 1B, RX: 448M)
[--] Reads / Writes: 38% / 62%
[--] Total buffers: 6.2G global + 4.5M per thread (151 max threads)
[OK] Maximum possible memory usage: 6.8G (2% of installed RAM)
[OK] Slow queries: 0% (0/1M)
[OK] Highest usage of available connections: 12% (19/151)
[OK] Key buffer size / total MyISAM indexes: 16.0M/101.0K
[OK] Key buffer hit rate: 100.0% (372K cached / 7 reads)
[OK] Query cache efficiency: 56.8% (327K cached / 576K selects)
[OK] Query cache prunes per day: 0
[OK] Sorts requiring temporary tables: 0% (1 temp sorts / 145K sorts)
[!!] Temporary tables created on disk: 47% (116K on disk / 244K total)
[OK] Thread cache hit rate: 99% (19 created / 7K connections)
[OK] Table cache hit rate: 55% (753 open / 1K opened)
[OK] Open file limit used: 0% (48/20K)
[OK] Table locks acquired immediately: 100% (1M immediate / 1M locks)
[OK] InnoDB data size / buffer pool: 43.2M/4.0G

-------- Recommendations -----------------------------------------------------
General recommendations:
    Run OPTIMIZE TABLE to defragment tables for better performance
    Temporary table size is already large - reduce result set size
    Reduce your SELECT DISTINCT queries without LIMIT clauses